This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. For nascent proteins destined for excretion or membrane insertion, synthesis by the ribosome is concomitant with their insertion into a protein-conducting membrane channel, SecY, which translocates a protein across or inserts it into the membrane. In collaboration with cryo-electron microscopists we determined an all-atom structure of a ribosome-SecY-nascent-protein intermediate that permits one to investigate the membrane insertion pathway. We seek to simulate the membrane-SecY-nascent protein part of our structure to determine how the intermediate revealed, an orientationally inverted N-terminus binding outside a SecY lateral gate, arises from forces due to protein elongation.